The present invention relates to an engine control system and method and more particularly to a method for estimating barometric pressure for use in a direct injection stratified charge (DISC) engine control scheme.
Gasoline DISC engine technology has the potential of improving fuel economy through the use of stratified combustion, which significantly extends the lean burn limit and reduces pumping losses in the engine. Compared with a conventional port fuel injection (PFI) gasoline engine, a DISC engine is more complicated in its hardware and operating strategy. Like a PFI engine, a DISC engine consists of an intake manifold, combustion chambers, and an exhaust system. Its hardware design and configuration, however, are different from a PFI engine in several key aspects.
A DISC engine can effect two distinct modes of operation by properly timing the fuel injection in relation to other engine events. By injecting early in the intake stroke, there is enough time for the mixing of air and fuel to form a homogeneous charge by the time the ignition event is initiated. On the other hand, by injecting late in the compression stroke, the special combustion chamber design and the piston motion will lead to the formation of a stratified charge mixture that is overall very lean, but rich around the spark plug.
Changes in altitude result in changing ambient air pressure which, in turn, affects the density of air. Air density limits the amount of air change and, hence, available engine torque at a given engine speed and throttle position. Therefore, it is preferable to have barometric pressure information available to the engine controller so that adjustments can be made accordingly to prevent performance degradation.
Furthermore, barometric pressure sensors add cost to the vehicle. Thus, it is desirable in both port fuel injected (PFI) and DISC engines to have a robust control scheme without the need for a barometric pressure sensor and provides a robust estimate of barometric pressure for all engine operating conditions.
It is an object of the present invention to provide an improved engine control method that eliminates the need for a barometric pressure sensor and provides a robust estimate of barometric pressure for all engine operating conditions.
The foregoing and other objects are attained by a method of continuously estimating barometric pressure values for use in an engine control system. The vehicle includes an manifold absolute pressure (MAP) sensor, ambient air temperature sensor and a throttle position sensor. The method comprises the steps of determining the manifold absolute pressure, ambient air temperature, and throttle position. When the throttle position is at wide-open throttle, the method generates a barometric pressure value {circumflex over (P)}anew as a function of the manifold absolute pressure value (P). Otherwise, the method generates a barometric pressure value as a function of the manifold absolute pressure value (P), and an estimated intake manifold pressure {circumflex over (P)}and estimated mass airflow .
In a further embodiment, the vehicle includes a manifold absolute pressure (MAP) sensor, mass airflow sensor (MAF), ambient air temperature sensor and a throttle position sensor. The method comprises the steps of determining the manifold absolute pressure, mass airflow, ambient air temperature, and throttle position. When the throttle position is at wide-open throttle, the method generates a barometric pressure value {circumflex over (P)}anew as a function of the manifold absolute pressure value (P). Otherwise, the method generates a barometric pressure value as a function of the manifold absolute pressure value and mass airflow value .
An advantage of the present invention is that it eliminates the need for a barometric pressure sensor and thereby reduces the overall vehicle cost. Another advantage is that it provides a robust estimate of barometric pressure for all engine operating conditions, including partial load and WOT.
Other objects and advantages of the invention will become apparent upon reading the following detailed description and appended claims, and upon reference to the accompanying drawings.